As the integration density of semiconductor devices increases, the lithographic process requires higher resolution to meet the precision requirements of the semiconductor devices. Photolithography process is typically used to fabricate electronic and optoelectronic devices on a semiconductor substrate and photoresist patterns prepared by the photolithography process are used as masks in etching or ion implantation. Therefore, the fineness of the photoresist patterns is a very important factor in determining the degree of integration.
One method to increase resolution is to use a light source with a shorter wavelength as the exposure light source. For example, a krypton fluoride (KrF) laser is used to provide deep UV light with a wavelength of 248 nanometers and an argon fluoride (ArF) laser is used to provide deep UV light with a wavelength of 193 nanometers. Another method of forming such fine photoresist patterns on the semiconductor substrate is through double patterning technique. In a double patterning process, a pattern from a first exposure may be etched onto a photoresist layer on the semiconductor substrate, and the semiconductor substrate is subsequently recoated with the photoresist layer to form a second pattern and then re-etched to obtain the desired pattern. However, the double patterning technique requires that the exposure process be performed twice, which requires very precise alignment between the two exposure processes.
This Discussion of the Background section is provided for background information only. The statements in this Discussion of the Background are not an admission that the subject matter disclosed in this section constitutes prior art to the present disclosure, and no part of this Discussion of the Background section may be used as an admission that any part of this application, including this Discussion of the Background section, constitutes prior art to the present disclosure.